How worried should we be if astronomers were to report finding an asteroid that could collide with Earth 50 years from now? Planetary scientist Richard Binzel of the Massachusetts Institute of Technology has devised the Torino Impact Hazard Scale as a handy tool for scientists, the media and a public confused by a number of recent false alarms (see Nature 392, 215; 1998).

Catastrophe or no? Binzel's Impact Hazard Scale will tell us.

Similar to the Richter scale used to rank earthquakes, Binzel's scale plots the energetic ‘wallop’ packed by an incoming asteroid against the likelihood that it will hit Earth, and assigns numerical values ranging from zero (virtually no chance of damage) to ten (certain catastrophe) to each event.

Adopted last month at a workshop of the International Astronomical Union in Torino, Italy, the idea was endorsed last week by the full union.

The reviews so far have been good. Carl Pilcher, head of NASA's planetary science programme, called it “a major advance in our ability to explain the hazard posed by a particular object”. Binzel hopes his scale will bring discipline to the reporting of impact hazards. “Scientists haven't done a very good job of communicating to the public,” he says.